The present invention relates generally to an apparatus for processing a vapor fuel of a lean-burn internal combustion engine capable of burning an air-fuel mixture which is in an over-oxygen state, and more particularly to a technology of processing the vapor fuel without disturbing a state of the air-fuel mixture when executing a lean-burn.
In an internal combustion engine mounted in an automobile and the like, for reducing a fuel consumption, there has been increasingly developed in recent years a lean-burn internal combustion engine capable of burning an air-fuel mixture of which an air-fuel ratio is higher than a theoretical air/fuel ratio (which implies an over-oxygen state). What is known as this type of lean-burn internal combustion engine is, e.g., a cylinder injection type lean-burn internal combustion engine, wherein a fuel injection valve is attached so that an injection hole thereof faces an interior of a combustion chamber.
The cylinder injection type internal combustion engine is constructed such that fresh air is, in a low-load operation region, introduced into the combustion chamber at an intake stroke, and at a subsequent compression stroke the fuel is injected from the fuel injection valve, and a combustible air-fuel mixture is formed only in the vicinity of a spark plug. That is, the air-fuel mixture in the combustion chamber is brought into so-called a stratified state in which a combustible air-fuel mixture layer is present in the vicinity of the spark plug, and an air layer is present in other areas. The stratified air-fuel mixture is burned, wherein the combustible air-fuel mixture layer being present around the spark plug serves as an ignition source.
Further, the cylinder injection type internal combustion engine is constructed such that the fresh air is, in an intermediate-load operation region, introduced into the combustion chamber at the intake stroke, and simultaneously the fuel is injected from the fuel injection valve. On this occasion, a quantity of the fuel injected from the fuel injection valve is such a quantity that a ratio of the fresh air to the fuel quantity (which is so-called an air-fuel ratio) is higher than a theoretical air-fuel ratio. In this case, there is formed a lean air-fuel mixture in which the fuel is uniformly mixed with the fresh air substantially over the entire area within the combustion chamber.
Further, according to the cylinder injection type internal combustion engine, in a high-load operation region, the fresh air is introduced into the combustion chamber at the intake stroke, and the fuel is injected from the fuel injection valve. On this occasion, the quantity of the fuel injected from the fuel injection valve is such a quantity that the ratio of the fresh air to the fuel quantity (which is so-called the air-fuel ratio) is substantially equal to the theoretical air-fuel ratio. In this case, there is formed a stoichiometric air-fuel mixture in which the fuel is uniformly mixed with the fresh air over the entire area within the combustion chamber.
As described above, the cylinder injection type internal combustion engine is capable of actualizing the lean burn in the low- and intermediate-load operation regions, whereby the fuel consumption can be largely reduced.
On the other hand, the internal combustion engine is provided in combination with a vapor fuel processing apparatus for processing the vapor fuel produced in a fuel tank and the like. This vapor fuel processing apparatus is constructed of a charcoal canister for temporarily reserving the vapor fuel produced in the fuel tank, an atmospheric air introducing passageway for introducing the atmospheric air into the charcoal canister, a negative pressure introducing passageway for introducing into the charcoal canister an intra intake pipe negative pressure produced in an intake passageway disposed downstream of a throttle valve, and a flow rate control valve provided at the negative pressure introducing passageway.
In the thus constructed vapor fuel processing apparatus, when the flow rate control valve is closed, the vapor fuel produced in the fuel tank is adsorbed to an adsorbent such as an activated carbon and the like charged in the charcoal canister.
In the vapor fuel processing apparatus, when the flow rate control valve is opened, the intra intake pipe negative pressure produced in the intake passageway is applied to the charcoal canister via the negative pressure introducing passageway. When the intra intake pipe negative pressure is applied to the charcoal canister, the atmospheric air is sucked into the charcoal canister via the atmospheric air introducing passageway, and subsequently sucked into the intake passageway via the negative pressure introducing passageway. Thus, according to the vapor fuel processing apparatus, when the flow rate control valve is opened, there is formed a flow of the atmospheric air flowing through the charcoal canister.
With the through-flow of the atmospheric air, the vapor fuel which has been adsorbed to the adsorbent desorbs therefrom and is guided together with the atmospheric air to the intake passageway. The vapor fuel and the atmospheric air guided to the intake passageway are further guided to the combustion chamber of the internal combustion engine while being mixed with the fresh air flowing from upstream of the intake passageway. Then, the vapor fuel and atmospheric air are, together with the fuel injected from the fuel injection valve, are burned and processed.
Here, it can be considered that the vapor fuel processing apparatus is applied to the cylinder injection type internal combustion engine. However, in this case, if the vapor fuel is introduced into the intake passageway from the charcoal canister when the cylinder injection type internal combustion engine is in a stratified charge combustion operational state, the inside of the combustion chamber is not developed into a stratified state, or alternatively a combustible air-fuel mixture layer becomes an over-fuel state, because the vapor fuel is supplied into the combustion chamber while being mixed with the fresh air. Thus, it is possible to cause deteriorations of a combustion state and of an emission to out of an allowable level.
To cope with such a problem, there has hitherto been proposed a cylinder injection type internal combustion engine disclosed in Japanese Patent Application Laid-Open Publication No.4-194354. In this cylinder injection type internal combustion engine, the vapor fuel is supplied to the intake passageway only when the engine load is larger than a predetermined qualified load. That is, the vapor fuel is supplied to the intake passageway only when the internal combustion engine is in a uniform combustion operational state, and the vapor fuel is to be processed without destabilizing the combustion.
However, the cylinder injection type internal combustion engine disclosed in the above-mentioned Japanese Patent Application Laid-Open Publication No.4-194354 executes the purging of the vapor fuel so long as the engine operational state is in a uniform combustion operation region, and is, therefore, incapable of processing all the vapor fuel reserved in the charcoal canister, and the charcoal canister might be saturated.